The present invention provides a steel composition. More specifically, a composition for a low-alloyed steel with a low to medium carbon content is disclosed, which steel is suitable for casting into components to meet specifications of the Association of American Railroads (AAR) for such railroad car components. This steel composition provides improved mechanical and physical properties over the compositions of steel materials currently utilized to meet these AAR railway car component specifications, as well as providing improved weldability, higher impact strength and notch toughness.
A large number of railway car components are produced under AAR specification M-201 for Grades A and B steel, which has the following composition requirements: 0.32% Carbon (maximum); 0.90% Manganese (maximum); 0.04% (maximum) Phosphorous; 0.04% (maximum) Sulfur; and, 1.50% (maximum) Silicon. Another AAR specification for railway car components, mechanical property test 7.2 (7.2.2), requires a minimum tensile strength of 70,000 psi, a minimum yield strength of 38,000 psi, an elongation in 2 inches of 24%, and a reduction in area of 36%. These specifications are largely directed to cast shapes and parts. The shapes or structures cast from such steel materials have been known to be utilized in the as-cast state, however, the cast shapes or structures are frequently normalized to produce a more uniform grain structure. In addition, these materials may have an unspecified requirement to provide weldability, as the cast shapes are frequently coupled or connected to other members by weldments.
Elevated carbon concentration in steel materials will or can interfere with their weldability. Welded members can experience "hot-cracking" at the weldment, which can result in failure and fracture. As a consequence, materials and casting suppliers provide products conforming to the above-noted AAR compositional and physical property specifications while they strive to minimize the carbon concentration in the steel material.
The mechanical strength of steel and its products can be improved by the addition of alloying elements, such as nickel, chromium, vanadium, molybdenum, boron and other alloying elements. These alloy additions must be judiciously chosen to minimize the increased costs from the alloying additions, and in consideration of the consequent change in the steel's physical and chemical properties from such additions. More specifically, the indiscriminate addition of alloying elements may positively affect some physical properties but may diminish or degrade other properties. As an example, a boron addition can increase the hardness of some steel grades, but such an addition may reduce the elongation or increase the brittleness of the steel. Other additions can be deleterious to the weldability of a steel alloy. Any alloying element addition is, or can be, costly in terms of raw material expense and added production labor costs, but further costs may be incurred from special subsequent treating or machining of products manufactured from these materials. Consequently, steel alloys may be provided to meet the requirements for a specific application, which requirements are not met by existing grades of steel, either alloy of common grades, but the alloy selection must be directed to the the desired physical and chemical characteristics for the application.